The inventive subject matter relates to electric power systems and methods of operating the same and, more particularly, to power system control apparatus and methods.
Islanded power systems include systems that may be isolated from a utility grid. Such system may include, for example, systems served by uninterruptible power supply (UPS) systems, motor-generator sets, fuel cells, and the like. Typical uninterruptible power supply (UPS) systems are designed to provide uninterrupted power to a protected load by transferring the load from a failed primary source, such as a utility line, to a secondary source, such as a battery, flywheel, fuel cell or the like. UPS systems may also be interfaced to other energy sources, such as motor/generator sets, microturbines, wind-powered generators, and photovoltaic arrays. UPS systems may have a variety of different architectures, including on-line (double conversion), standby and line-interactive. Various different converter (e.g., inverter) architectures may be used in other types of islanded power systems.
Data centers commonly use UPSs in their power distribution systems to ensure a desired level of availability. These power systems may have a variety of different configurations of power sources (e.g., gensets, photovoltaic arrays, batteries and the like), UPSs and interconnecting switchgear. For example, some data center power systems may include a combination of one or more UPSs that provide short-term backup power and one or more diesel and/or natural gas fired generators that provide longer-term backup power. These various power system arrangements may provide various levels of availability. A tiered availability scheme for data centers is defined by the Uptime Institute and described at www.uptimeinstitute.com.
Some systems use redundant UPS arrangements wherein one UPS may be used to back up another UPS. For example, some systems may utilize parallel redundant arrangements in which two or more UPSs (or UPS modules) are connected in parallel to a common bus, with the paralleled system having a capacity sufficiently greater than a maximum projected load to provide redundancy. Other systems may use an isolated redundant arrangement in which one or more primary UPSs serve respective protected loads (e.g., respective server rack rows in a data center) and one or more reserve or “catcher” UPSs is configured to pick up a protected load in the event of a failure (e.g., hardware and/or capacity) of its serving primary UPS. Other types of redundant UPS arrangements are described, for example, in U.S. Pat. No. 8,850,237 to Familiant et al. These UPS arrangements may be further backed up by generators or other power sources.